Definitely do not sell yourself short. If you are cheap, they will wonder is he worth it?
The first time I charged for tutoring I thought 25$ was way too high and I was told as 40$ was the going rate in my area, that is why I did not get as many clients (though I am a certified teacher in that subject)
Find out what others in your area/state if you are in the US charge and use that as a guide.